The present invention relates to a powdery material of minute composite ceramic particles having a dual structure, comprising the core formed of zirconium oxide and the outer shell formed of aluminum oxide, a process for producing thereof and an apparatus for producing thereof.
Generally, processes for producing a powdery material of minute ceramic particles in gas phase have been known (refer to "Bulletin of the Ceramic Society of Japan", Vol. 13, No. 8, pages 625-633, 1978). For instance, while using a vapour of an easily vaporizable compound such as metal halides, minute particles of an oxide of the metal are formed by reacting the vapour with oxygen or water vapour. Minute particles of a nitride of the metal and minute particles of a carbide are produced by the similar processes of reacting the vapour with nitrogen or ammonia and a hydrocarbon such a methane, respectively. Since the thus formed minute particles are very small in size, they are excellent in sinterability and are suitable for preparing ceramics of high strength and excellent performance.
As a result of study on gas-phase processes for producing a powdery material of minute composite ceramic particles with two components, the present inventor has found that it is possible to produce a powdery material of minute composite ceramic particles having a dual structure, wherein the component of the core and the component of the outer shell(hull) are different from each other by selecting the respective positions of the inlets for the introduction of the two metal halides into the combustion chamber as a reaction chamber and the shape of the combustion chamber, and has attained to the present invention. According to the present invention, zirconium chloride, especially zirconium tetrachloride is preferably used as the raw material for forming the core and aluminum chloride is used and the raw material for forming the outer shell. It has been confirmed by the present inventor that the ceramic material obtained by sintering the thus produced powdery material of minute composite ceramic particles (powdery material) having a dual structure according to the present invention shows remarkably improved performances as compared to the ceramic material obtained by sintering a mixture of zirconium oxide and aluminum oxide prepared by a conventional simple mixing technique.